I should begin here: During the actual '90s, I was much too busy listening to Japanese videogame soundtracks (educate yourself) to actually enjoy '90s pop music. My first-hand memories of most of it are hearing it in a car, at a skating rink, on somebody else's Discman, and shaking my head in lonely disapproval because the lyrics were in English. I love all of it now -- it feels, in hindsight, like I always have -- but I am not the right man for the job of overgeneralizing every pop song from the '90s into neat, reductive categories.
Which is why I'm only going to start doing that. For the purposes of explaining to someone you've just met at a party which '90s music you like; for the purposes of chaos dunking on somebody when they act like their love of Candlebox is as cool as your love of Fastball; for the purposes of having pleasant, dreamy conversations with demographically appropriate companions about songs you first heard in the middle seats of a minivan, I humbly offer a few starter categories for the '90s pop songs you kind of remember enjoying, for use when you and a friend go on a YouTube binge some boring weekend night.
Please add more in the comments, as they occur to you. This is only a start, and I am only one man. One man whose favorite CD in 1999 was the soundtrack to Super Mario 64.